In certain processes such as chemical vapor deposition (CVD) with chemical reactions of gases inside a high temperature furnace, pre-heating of source gases during delivery to the furnace is often needed to maintain the source gases at a certain temperature. Those processes are typically highly sensitive to contamination, especially when they are used for semiconductor manufacturing or other nano-technologies. Heating elements in the equipment that easily react, corrode, or generate particles affect the source gases and consequently lower the yield of the end products. Those processes often require a clean room environment where the space to install apparatuses is limited as the room size is an important factor that determines the running cost. Among the apparatuses that provide such a function, downsizing and contamination reduction are common goals.
At elevated temperatures, most of commonly used metal materials become a potential source of metal contamination. In such an environment, the use of quartz to encase a heater element is known in the art to overcome the contamination problem. U.S. Pat. No. 6,868,230 discloses a vacuum insulated heater assembly, wherein the heating element or heater is a quartz glass tube. The vacuum effectively insulates the heating part from the environment and protects the heating element from oxidation. However, the prior art quartz tube heater is quite often bulky and not energy-efficient. The heat transfer through the channel wall of the passage is not the most efficient since, with the tubular flow passage implied in the prior art, the bulk of the flow passes near the center of the tube where the flow is the furthest from the heated surface in the passage.
There is still a need for an improved heater assembly, wherein the heating element is self-contained within the vacuum insulated heater assembly. The invention relates to an improved vacuum heater which is energy efficient, providing heat to the source gases in a range of laminar flow with reduced risk of contamination.